Winning return – Nadal made his comeback after seven months away from the ATP World Tour with a doubles win on Tuesday.

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Rafael Nadal returns in Chile7 photos

Second seeds beaten – Nadal teamed up with his friend Juan Monaco to win their doubles match against Czech Republic's Frantisek Cermank and Lukas Dlouhy in a Chilean claycourt event.

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Rafael Nadal returns in Chile7 photos

Knee problems – Nadal has had problems with his knees for much of his career. His latest absence was caused by an injury to the left one, which required surgery.

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Rafael Nadal returns in Chile7 photos

Low expectations – He told reporters before the tournament that he expects it will take him several weeks to regain match fitness.

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Rafael Nadal returns in Chile7 photos

Important meeting – Nadal arrives at La Moneda presidential palace in Santiago on February 1.

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Rafael Nadal returns in Chile7 photos

President Pinera – He was received by Chilean president Sebastian Pinera ahead of his debut appearance at the Vina del Mar Open.

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Story highlights

Rafael Nadal wins on his return to singles action

The former world No. 1 beats Argentine Federico Delbonis 6-3 6-2

The 11-time grand slam winner has been out for seven months with a knee injury

The Spaniard made his return in a doubles victory on Tuesday

Former world No. 1 Rafael Nadal was back in singles action for the first time in seven months Wednesday, making a winning return on the clay courts he has dominated so emphatically in recent years.

Having not played a singles match since his shock defeat to Lukas Rosol in the second round of Wimbledon last year due to a left knee injury, a little rustiness was perhaps to be expected.

But, after losing the first two games of his match with Argentine Federico Delbonis, the 11-time grand slam champion recovered to record a morale-boosting 6-3 6-2 victory in the second round of the Chile Open in Vina del Mar.

"I'm happy to play a singles match after so long," the 26-year-old told the ATP World Tour's website. "I need days and time to get my game back, but so far the feeling on court is great."

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Super Novak – Novak Djokovic has become the world's top tennis player since overhauling his diet in 2010. "I observed him playing in the Australian Open," says the Serbian's former nutritionist Dr. Igor Cetojevic. "The commentator repeatedly referred to 'his asthma' and the problems he had breathing."

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How to supercharge your body11 photos

Go gluten, go – However, Cetojevic said the problem was Djokovic's intolerance to gluten -- which is found in grains such as wheat and their byproducts -- so he had to eliminate it from his diet and add more fruit, rice, vegetables and fish protein. The Serbian has now won a record three successive Australian Open titles.

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How to supercharge your body11 photos

Before – This image, provided by Australian naturopathic physician Hamish Everard, shows what blood looks like before going on a gluten-free diet. The cells are clumped closely together.

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After – This image, taken after the subject went on a gluten-free diet, shows the blood cells are able to flow more freely -- allowing better transportation of oxygen around the body.

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Immediate benefits – "After eliminating grains from the patients' diet, all of their symptoms began to resolve within only a few days," says Everard. "Not only did their gastrointestinal symptoms disappear, but so too did other metabolic symptoms such as chronic and general fatigue, diabetes (high and low blood sugar), high cholesterol, decrease in inflammatory markers, soft tissue injuries, joint pain and stiffness, improved cognition (concentration), less anxiety, decreased depression, increase in bone density in osteoporosis patients, eczema, psoriasis and a decrease in acidity levels."

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The price of 'progress' – Experts say many health problems stem from changes in food production. "The hybridization of the native European wheat with a shorter, hardier strain from South America in the 1940s produced the particular gluten protein that triggers the sensitivity in people's digestive system," says Cetojevic. "For thousands of years people ate and digested wheat without adverse effects, but we haven't yet adapted to the new protein in the hybrid variety that is now widely grown and marketed for its convenience and higher yield. People are better off eating the older strains such as spelt and kamut."

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Learning to change – Pasta is another staple food for many athletes. "Educating people on long-term dietary habits often depends upon how bad they felt before," says Everard. "The worse you were, the more willing you are to make the change. Athletes are disciplined and often do whatever is required of them to improve physically, mentally and emotionally for their sport. I try to teach the 80/20 principle: 80% good 20% bad. Once the underlying causes of gluten intolerance has been corrected, most patients can consume it again in some form or another."

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Enemy inside – People who are gluten intolerant suffer damage to their intestinal microvilli. "We have seen a definite link in gluten intolerant patients as far as a decrease in beneficial stomach bacteria, an increase in acidity and a decrease in both gastric digestive enzymes and pancreatic enzymes," says Everard.

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Restoring the flora – Probiotics are used to repair the chronic inflammation caused by leaky gut. "We monitored our patients and found that when they did extensive exercise 82% showed symptoms of gut discomfort, reduced tolerance to the heat or a decrease in immune function," says Everard. "Probiotics (good bacteria) protect the gut and decrease this leaky gut/intestinal permeability, therefore improving athletes' performance, stamina, immunity, electrolyte balance and digestion of proteins (especially gluten and dairy)."

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Hidden dangers – Like his childhood friend Djokovic, U.S. Open champion Andy Murray has also gone gluten-free. This cake he received for his 25th birthday, even if made without wheat, could still be problematic for his diet as an elite performer due to any processed sugars and dairy in the ingredients. "Hamish's protocols basically remove sugar and the gluten from your diet, sometimes the dairy, to help cleanse and restore the hormonal system and the digestive system," says tennis coach Pete McCraw. "It's the gut flora that the sugar plays havoc with, it changes the bacteria levels in the stomach, which for some athletes, means they digest food inefficiently."

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Changing times – Cetojevic believes the trend towards gluten-free diets is growing. "In 2011 I saw that most of the players' lounges on the tennis circuit offered gluten-free options, which was not the case in 2010," he says. "I observed that some of the top players have slimmed down and are faster on the court."

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EXPAND GALLERY

The Spaniard, who has dropped to fifth in the world rankings during his long absence, made his much-anticipated return in a doubles match Tuesday.